This work is directed to the study of exocrine secretion on a cellular level in two different systems. The first system entails the correlation of in vitro amylase secretion by dissociated parotid gland parenchyma (biochemical cross-sectional data) with the kinematic activity of acinar cells stimulated in microchambers during cinemicrographic recording (histometric longitudinal data). Results suggest that at the acinar level the secretion rate accelerates in the first ten minutes, remains at a steady rate for five to eight minutes, and finally decelerates so that at twenty-five minutes the cells are depleted of secretion granules. Simultaneously, cells and whole acini demonstrate rhythmic contractions and the acinar lumen enlarges, reaching its greatest size fifteen minutes after stimulation after which it becomes reduced once again. The second system entails the study of the secretory cells responsible for byssus formation in sea mussels. Mytilus secretes structural proteans and other substances which form a tough extra- organismal structure resistant to degradation in the marine environment. Ultrastructural studies demonstrate that partly polymerized collagen is accumulated in secretion granules, secreted by merocrine exocytosis and fully polymerized in the presence of polyphenolic compounds plus polyphenol oxidase. The formation of terminal adhesive discs and the proximal byssus stem are also under study.